Immunology

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Immunology is a broad branch of biomedical science that covers study of all aspects of the immune system in all organisms. It deals with, among other things, the physiological functioning of the immune system in states of both health and disease; malfunctions of the immune system in immunological disorders (autoimmune diseases, hypersensitivities, immune deficiency, allograph rejection); the physical characteristics of organs in the immune system; and in vitro, in vivo and in situ chemical and physiological properties of biological components of the immune system. Immunology has various applications in several disciplines of science, and as such is further categorised accordingly.

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Histological examination of the immune system

Before even the concept of immunity was developed numerous early physicians characterised organs that would later prove to be part of the immune system. The key organs of the immune system are the thymus, spleen, bone marrow lymph nodes (including major lymph nodes such as tonsils, and adenoids), lymph vessels and various tissue associated lymphoid tissues. The major organs, the thymus and spleen, are really only histologically examined post-mortem during autopsy. However some lymph nodes, and accessory lymphid tissue can be surgically excised for examination while patients are still alive.

Many components of the immune system are actually cellular in nature and not associated with any specific organ, but imbedded or circulating in various tissues located about the body.

Classical immunology

Classical immunology ties in with the fields of epidemiology and medicine. It studies the relationship between the body's systems, pathogens and immunity. The earliest written mention of immunity can be traced back to the plague of Athens in 430 BC. Thucydides noted that people who had recovered from a previous bout of the disease could nurse the sick without coming down with the illness a second time. Many other ancient societies have references to this phenomenom but it was not until the 19th and 20th centuries before the concept developed into scientic theory.

The study of the cellular and molecular components that comprise the immune system, including their function and interaction is the central science of immunology. The immune system has been divided into innate immune responses, and adaptive immune responses, the latter of which is further divided into humoral and cellular components.

The mainstay of classical immunology has been the interaction between antibodies and antigens. Without an understanding of the properties of these two biological entities, much of immunology would be non-existent.

In the 21st century though, immunology has broadened its horizons with much reserach being performed into more specialised niches of immunology. This includes the immunological function of cells, organs and systems not normally associated with immunology, as well as the function of the immune system outside of clasiscal models of immunity.

Clinical immunology

Clinical immunology is the medical field that deals specifically with disease caused by the immune system, and diseases of the immune system. This includes various disorders ranging from hypersensitivities such as asthma to immunodefiencies such as Acquired Immunodeficiency Syndrome (AIDS). Additional autoimmunity and transplant rejection falls into this category.

Immunotherapy

See main article Immunotherapy

The use of immune system components to treat a disease or disorder is known as immunotherapy. Immunotherapy is most commonly used in the context of the treatment of cancers as an adjuvant to chemotherapy (drugs) and radiotherapy (radiation). However, immunotherapy is often used in the immunosuppressed (such as HIV patients) and people suffering from other immune deficiencies.

Immunotherapy has also been successful in the alleviation of allergies.

Diagnostic immunology

The specificity of the bond between antibody and antigen has made it an excellent tool in the detection of substances in a variety of diagnostic techniques. Antibodies specific to a desired analyte can be conjugated with a radiolabel, fluorescent label, or color-forming enzyme and used as a "probe" to detect the analyte.

Well known applications of this include immunoblotting, ELISA and immunohistochemical staining of microscope slides. The speed, accuracy and simplicity of such tests has led to the development of rapid techniques for the diagnosis of disease, microbes and even illegal drugs in the nevironment as opposed to in the laboratory (of course tests conducted in closed environmnet have a higher degree of accuracy). Such testing is also used to distinguish compatible blood types.

Evolutionary immunology

Study of the immune system in extant and extinct species is capable of giving us a key understanding of the evolution of species on Earth.

A hierachy of immunity can be seen from simple phagocytotic protection from single celled organisms, to circulating antimicrobial peptides in insects to lymphoid organs in vertebrates. Of course, like much of evolutionary, this is often seen from an anthrocentric ("humans are best") model of evolution, but it must be recognised, that every organisms immune system is absolutely capable of protecting it from most forms of harm.

Insects and other arthropods, while not possessing true adaptive immunity, show highly evolved systems of innate immunity, and are additionally protected from external injury (and exposure to pathogens) by their chitinous shells.

Additionally vertebrate and mammalian systems show a high degree of differentiation between there immune systems compared to other bodily systems. This can present a problem when trying to extrapolate experimental results from animal models (often mice onto humans.

Innate immunity

There are two broad, artificial subdivisions of mammalian immune systems: the innate (or natural) and the acquired (or adaptive). The innate immune system is usually meant to encompass cells and systems in the mammalian immune system that does not require previous exposure to a particular pathogen for function.

Study of these focuses often on errors of the immune system, which often cause more damage than what they are detecting and reacting to. In effect, the immune system is what decides "what is part of this body" by ignoring its intervention. Some infections, like HIV exploit the limits or weaknesses of the human immune system very effectively and able to make themselves part of the body. Artificial means are often used to restore immune system function in an HIV-challenged body, and prevent the onset of AIDS. This is one of the most complex issues in immunology as it involves literally every level of that system. This research during the 1980s and 1990s radically changed the view of the human immune system and its functions and integration in the human body.

Acquired immune response

The acquired immune system encompasses cells and systems that require previous exposure, and explains the somewhat unique ability of the mammalian immune system to 'remember' previous infections and mount a rapid and robust reaction to secondary infections. This immunological memory is due to the biology of T-cells and B-cells.

Herd immunity for instance is acquired by organisms living close together sharing minor infections all the time.

Vaccines boost the acquired immune system by offering weak forms of infection that the body can fight off and remember how to do so - when a stronger infection arises the body thus fights it off readily.

The distribution of vaccines and other immune system affecting cures can be considered another level of acquired immune system, one governed by access to vaccination and medicine in general. The intersection of this with the spread of disease (as studied in epidemiology) is part of the field of public health.

Integrated immune response

The natural or innate immune system of the human body is linked very deeply and directly to the nervous system and sensory system, a link first explored by studies on epilepsy. An epileptic attack is actually an immune system reaction triggered by a purely sensory or nervous input, like a strobe light. There are also studies of long term HIV survivors which suggest very strongly that psychology is a key healing factor and that it is quite possible to survive long term with very low immune system function if one avoids major psychological stress and stays quite calm and optimistic regardless of news. This might be because of the immune system's tendency to panic under conditions of high stress, to the detriment of the organism, sometimes attacking it from the inside.

Because of these issues, a view is evolving of a single system that responds cognitively to perception, physiologically with pain via nerves, and immunologically with the more chemical elements of the immune system that float free in the human bloodstream. The study of this system is psychoneuroimmunology.

See Also

References

Goldsby RA, Kindt TK, Osborne BA and Kuby J (2003) Immunology, 5th Edition, W.H. Freeman and Company, New York, New York, ISBN 0-7167-4947-5[[es:Inmunolog�a]]


References

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